And perhaps a longer solar cycle.

The sunspot cycle maybe part of a longer activity period, says Richard Altrock, a U.S. Air Force scientist stationed at the National Solar Observatory facility at Sacramento Peak, N.M. He adds that successive solar cycles may overlap.

Altrock bases his conclusions on 19 years of data gathered at the NSO. The studies indicate the full solar cycle may last nearly two decades. Moreover, the cylce may embrace other types of magnetic activity besides visible sunspots.

The sunspots cycle, determined by the number and position of the spots, typically has an 11-year period. Increased sunspot formation at middle latitudes marks the beginning of each cycle. But other types of magnetic activity, which take place at higher latitudes - closer to the poles - precede sunspot formation, Altrock asserts.

Researchers had previously speculated that the solar activity cycle begins closer to the poles and then migrates to lower latitudes, Altrock notes. But high-latitude features on the surface of the sun are difficult to observe from Earth because the angle of sight distorts them or makes them invisible. To overcome this problem, Altrock and his colleagues restricted their observations to the corona, the region above the sun's visible surface. Since bright coronal features correspond to magnetic activity on the surface, the researchers could deduce the location of magnetic features on the sun.

Using a coronagraph to block the overwhelmingly bright light emitted by the solar surface, Altrock and his team measured faint emissions from the inner corona. Observations during the past 19 years by Altrock an others indicate that magnetic activity preceding the current sunspot cycle began at high solar latitudes in 1979. The full cycle is expected to last through 1998. The NSO studies also show that the next solar cycle, which should produce a peak number of sunspots just after the turnof the century, began in 1990 at a lattitude of 70 degrees, overlapping the current solar cycle. This cycle may also last about 19 years.